Hello, I purchased a 2003 E500 a few weeks ago and I ran into this issue that I can not find a solution too.

I purchased the vehicle in Portland and after the purchase I proceeded to drive it back to Seattle. After the 3-4 hour drive, I stopped at a friends house in Seattle. I turned off the car, went inside and was back out to the car within 5 minutes. When I went back out I put the key in the ignition and it would not turn. After trying multiple times I left it for 20 minutes, came back and it turned as it should. Later in the night, I went home and this issue happened again, except this time it would not start for over 2 hours. Then I realized every time I had been in it, I had the spare key in my pocket as well. Upon taking the spare key out of my pocket and trying again, it started right up. Brought the car up to Bellingham (where I go to school) and never had an issue with it. 3 weeks after the first incident, I am down in Seattle again (but had been there a week ago as well) and I run into the same issue, this time with no spare key, making me think that had nothing to do with it. I let it sit overnight one time and for an hour the other time. For both times it occurred over the weekend after the wait on each it started up.

The unlock/lock functions still work on the key it just will not start the vehicle. (by the way it is not the metal key if you haven't gotten that by now, it is one of the ones where you insert it.) I cant have this happen again and need to figure out the issue. I dont want to start replacing things because parts such as the EIS dont make sense because it isnt a constant issue. I am going to replace the batteries in the key today just because its cheap and will see if that works.

Also I do not know if this happened every time but on the most recent time I noticed while I was driving away that the error message "Malfunction Electrical Consumers switched off" appeared. However the A/C, audio, etc still was functioning.

Any help would be greatly appreciated, am seeing this issue across the threads but none exactly like this!

 

Im having the same exact issue but my only key fob I have stopped working suddenly after I tried changing the batteries due to the lock and unlock buttons stopped working on my key, I posted a more in depth explanation of my situation on a thread I posted since theres a lot that may have caused my issue but Im fairly new to this and have some sort of mechanical knowledge

 

I had to replace my EIS and it wasn't a constant issue either. Sometime it would start, other times it wouldn't. Seems unusual that the ignition won't turn. That's not evident in other posts that have described the EIS problem that I've seen. Search the W164 forum. There's a few experiences there that might assist.

 

Did you sort this?